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Ready line philosophy and implementation (RFC0642)

IP.com Disclosure Number: IPCOM000003713D
Original Publication Date: 1974-Jul-05
Included in the Prior Art Database: 2000-Sep-13
Document File: 3 page(s) / 8K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J.D. Burchfiel: AUTHOR

Abstract

BBN Report #1822, Specifications for the Interconnection of a Host and an IMP, gives a complete specification of the Host-IMP interface. However, the authors of this document bent over backward to avoid issuing arbitrary dictatorial directives to host interface implementors. They succeeded admirably in this goal by describing the IMP implementation, and suggesting similar behavior on the part of the host.

This text was extracted from a ASCII document.
This is the abbreviated version, containing approximately 35% of the total text.

Network Working Group Jerry Burchfiel

Request for Comments: 642 BBN

NIC: 30872 July 5, 1974

Ready Line Philosophy and Implementation

I. Introduction

BBN Report #1822, Specifications for the Interconnection of a Host

and an IMP, gives a complete specification of the Host-IMP interface.

However, the authors of this document bent over backward to avoid

issuing arbitrary dictatorial directives to host interface

implementors. They succeeded admirably in this goal by describing

the IMP implementation, and suggesting similar behavior on the part

of the host.

ARPA has appointed a PDP-11 local host interface standardization

committee composed of myself, Dave Retz of SCRL, and Yuval Peduel of

MIT Lincoln Labs. During our review of various interfaces designed

by the ARPA community, we have found total chaos, confusion and

misunderstanding about the recommended host interface implementation.

This note is an attempt to make explicit the recommendations which

are implicit in Report #1822. It provides a cookbook for interface

implementors, including a set of recommended do's and don't's in the

common problem areas. This document has been reviewed and approved

by the BBN IMP group.

II. Ready-line Philosophy

The following is an attempt to spell out in detail a consistent plan

for operation of the IMP ready line and host ready line with the

following objectives:

1. Reliably resynchronize and resume transmission after a

temporary lapse of service and possible loss of state

information by either system.

2. Make the programming of the host interface as simple as

possible. This will minimize bugs, and make it possible to

create a small ROM network-bootstrap loader.

First, consider the IMP ready line. When it drops, the IMP has

suffered a possible loss of state, so the message in transit from the

IMP to the host (if any) is likely to be incomplete. Similarly, the

message in transit from the host to the IMP (if any) is likely to be

incomplete. Both the host and the IMP must recognize this explicitly

by sending a message intended to be thrown away* (which may he

appended to the current message) and throw away the message currently

being received. (Both the host - IMP message and the IMP - host

message).

The simplest arrangement for the host's interface driver is a pair of

processes, one sending messages and the other receiving messages.

This drop of the IMP's ready line must be pr...